The train, which was heading to Savannah, Georgia, was carrying more than 340 passengers and seven crew members when it crashed.

An Amtrak passenger train crashed into the back of backhoe on the track causing the train to derail, killing two construction workers outside of Philadelphia on Sunday morning. The crash also left 35 people injured.

The train, which was heading to Savannah, Georgia, was carrying about 341 passengers and seven crew members, Amtrak confirmed. The impact caused the lead engine of the train to derail, CNN reported.

The names of those killed and details around their deaths won’t be revealed until after the Delaware medical examiner’s office have completed their autopsies after Monday.

Why this crash happened remains unknown. National Transportation Safety Board spokesperson Ryan Frigo told the press that they “are still gathering facts” and will be “looking into” a lot of potential factors.

U.S. Sen. Chuck Schumer told the Associated Press that this accident seems to be at the result of “human error.” He stressed, “There is virtually no excuse for a backhoe to be on an active track.”

Frigo agreed and said that he has no idea why the equipment was on the track either and that it would be part of the of the overall investigation, as will the speed of the train and other details.

Ari Ne’eman, a disability rights activist who was going to Washington D.C., said he was in the second car at the time of the crash. He told the AP, “The car started shaking wildly, there was a smell of smoke, it looked like there was a small fire and then the window across from us blew out.”

Cristine Starke, another passenger on the train, told CNN that the debris was so thick is “looked like snow on the windows.”

“I think we crumbled under the pressure. There’s a hole, and it looks as if the train bent, and that was about two feet in front of me. It felt like an explosion. I ended up on the ground,” she said.

Amtrak is no stranger to these types of horrific accidents. Just last month an Amtrak train heading from Chicago to LA derailed in Kansas and last year a derailment near Philly killed 8 and injured more than 200, CNN noted.